Let’s talk crank balancing

Discussion in 'Performance Mods' started by 45u, Apr 26, 2016.

  1. 45u

    45u Active Member

    I have built many a Harley crank including but not limited to rebuilding rods balancing the crank and assemble.
    Those doing balancing I am only guessing you are static balancing is this correct or does some make a way to dynamically balance these cranks?
    Are you balancing the cranks as a unit or do you take them apart and do each flywheel at a time by rotating and recuperating weight? If so what balance factor do you use? I like to do each wheel at a time as this gives much better results on Harley cranks. If you do both together then one wheel could be find the other off and you end up taking meat out of both meaning they will not be correct.
    Thanks
    Jeff
     

  2. 45u

    45u Active Member

    I have all so replace a many rod kit in 2 cycle motorcycle engines.
     
  3. jaguar

    jaguar Well-Known Member

    crank balancing with its "balance factor" is still in the Neanderthal age.
    For a more accurate scientific approach if you don't have a way to balance it dynamically (which also is neanderthal because it excludes the effect of engine compression) go to http://www.dragonfly75.com/motorbike/vibes.html and scroll about half way down
     
  4. 45u

    45u Active Member

    Do not tell those I balanced there cranks on motorcycles as I have done hundreds of them and all wore much better then before I balanced. OK so from what you are saying all the big crank guys are wrong including big companies like S&S. I know form experience on 4 cycles any how that using a balance factor works fine and been going it for 40 plus years. I have read your link before and will again.
    Thanks
    Jeff
     
  5. butre

    butre Well-Known Member

    working off a balance factor is kind of old school but it works well. a single cylinder cannot be dynamically balanced by nature.

    I find 60% to be a good all around balance factor, but that's for a motor that can hit 10,000 rpm without breaking a sweat so you really need to do this math yourself.
     
  6. 45u

    45u Active Member

    60% is what I use on street motorcycles. Do you understand how they dynamically balance a fly wheel crank? Any one journal crank are done all the same but takes time as you have to dissemble take the rods, bearings and cages out and install a bob weight. If you do no weighting or that I do not see how you can ever get it right! All I can figure is many just guess. I build street Harley s that run 8K (remember they are push rod motors) and the way I and MANY others do works fine. At 61 too old to change now. LOL
    Thanks
    Jeff

    http://www.darkhorsecrankworks.com/crankshaft_true.html
     
  7. butre

    butre Well-Known Member

    a lot of the cranks need to be trued more than anything, I've seen as much as 60 thou runoff in some of these piles of junk
     
  8. 45u

    45u Active Member

    WOW that is a lot and in its self would cause bad vibration. I do all mine with in .002 most of the time less. Truing is not a problem with all the cranks I have done over the years. Not able to use this on little cranks I use V blocks but this is what I use on big cranks to true. Might make a something to be able to use on little cranks if I get doing too many.

    [​IMG]

    This is one of my babies and use her often.
    [​IMG]

    A few of my percussion interments
    [​IMG]
     
  9. 45u

    45u Active Member


    Did not read it all but sure is much like I do it taking in the rotating and reciprocating weight. The way I do it is by numbers the way you do it is by guessing. Yes I agree different balance factors make a difference in different RPM ranges. There is not a perfect factor for all RPMs. This is why I balance race bikes and street bikes at a different factor. Will read more when I have time.
    Thanks
    Jeff
     
  10. jaguar

    jaguar Well-Known Member

    from my balancing page:
    "There is an old fashioned way of balancing the crank, with the peak RPM being a factor in how much weight should be removed from the counter-balance area. But in studying the subject I see that the main two forces that need to be counter balanced are changed in value of force equally as rpm increases so that rpm is not really a factor. That means that the correct flywheel counter-balance mostly depends on the upper assembly weight and dynamic cylinder pressure, not on rpm. Cylinder pressure changes non-linearly with rpm, mostly due to ignition timing. On my bike with the ignition timing curve of the Jaguar CDI it has the most cylinder pressure at around 6750 rpm."
     
  11. HeadSmess

    HeadSmess Well-Known Member

    tried finding a better pic, no luck...

    the only engine design that can be fairly well balanced for all speeds with only one piston.
    [​IMG]

    the piston follows a true sinusoidal curve. unlike conrods/crankshafts.
    these do become perfectly balanced in a 90 degree v twin layout.

    balancing is a joke.
     
  12. 45u

    45u Active Member

    Another of my passions live steam engines. At one time I use to have about 180 now I only have about 70. LOL My youtube videos.
    https://www.youtube.com/user/Jeff46u/videos
     
    Last edited: May 8, 2016
  13. 45u

    45u Active Member

    I am going to post some videos and links about balancing. I am not saying the way they do it is correct or not correct just want to get some input. All so on some of the videos read the below comments.
    Thanks
    Jeff

    <iframe width="420" height="315" src="" frameborder="0" allowfullscreen></iframe>
     
  14. 45u

    45u Active Member

    I do not see how you can get an accurate rotating and recuperating weight with out disassembling the crank?

    <iframe width="420" height="315" src="" frameborder="0" allowfullscreen></iframe>
     
  15. Fabian

    Fabian Well-Known Member

    a single cylinder engine with a conventional crankshaft-connecting rod cannot be balanced. It can only have the balance factor adjusted to minimise vibration in the most desired operational rpm range.
     
  16. 45u

    45u Active Member


    I disagree you can do a very good balancing job if you disable the crank. No a Harley is not a single cylinder but uses a male and female rod with only one cowmen crank pin and I balance them all the tine.l Been doing it for 40 plus years. To do these cranks I will have to machine mandrels for it.

    What do you thing balancing is? It is moving weight around or removing or adding to cut down on vibration.
     
    Last edited: May 20, 2016
  17. 45u

    45u Active Member

    This is on an earlier HD crank after all the weighting and figuring is done. Yes, it has removable shafts for the PTO and pinion but the later wheels have them made into the flywheel. But they do make mandrels for these wheels as well. These are what I am going to have to make as well as a adjustable bob weight. Like I said HD uses a cowmen crank pin with male and female rods.

    [FONT=Georgia, serif][/FONT]
     
    Last edited: May 20, 2016
  18. 45u

    45u Active Member

    Here is what I use to balance HD wheels.

    [​IMG]
     
  19. Fabian

    Fabian Well-Known Member

    You can balance the flywheel all you like, but when the single cylinder reciprocating components are attached, the engine cannot operate as a balanced assembly.

    You can have your opinion, but you are still wrong.

    A 45 degree Harley Davidson configuration cannot be properly balanced, unless the V-angle is opened up to 90 degrees.
    Honda did a lot of research into closing up the V-angle for it's premier 4-stroke motorcycle racing engine, to give an acceptable level of vibration, but 72 degrees is the tightest V-angle possible before balance becomes unacceptable, and a balance shaft is required.
     
    Last edited: May 20, 2016
  20. 45u

    45u Active Member

    How many cranks have you balanced? Have not done any bicyclist cranks YET but have done hundreds of HD cranks. The reciprocating weight is figure in to the bob weight!!!!!!!!!!!!!! Show me a lot about your knowledge as you do not have a clue. Only one way I to know for sure and that is do it myself! Prove me wrong since you think you know so much!!!!!!!!!!!!!!!!
     
    Last edited: May 20, 2016
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